β-Arrestins 1 and 2 differentially regulate LPS-induced signaling and pro-inflammatory gene expression

Toll like receptors, the critical receptor family in innate immunity, have been shown to signal via both ERK 1/2 and transcription factor NFκB. β-Arrestins 1 and 2 have recently been implicated in modulation of NFκB signaling and ERK 1/2 activation. Using a number of approaches: mouse embryonic fibroblasts (MEF) from wild-type (WT), β-arrestins knockouts (KO), β-arrestins 1 and 2 double KO, and MEFs with reconstituted WT β-arrestins in the double KO cells, RNA interference (siRNA) specific knockdown of β-arrestins, and overexpression of WT β-arrestins, it was demonstrated that β-arrestin 2 positively regulates LPS-induced ERK 1/2 activation and both β-arrestins 1 and 2 negatively regulate LPS-induced NFκB activation. Also β-arrestin 2 positively regulate LPS-induced IL-6 production and both β-arrestins 1 and 2 positively regulate LPS-induced IL-8 production. The specific ERK1/2 inhibitor PD98059 significantly decreased LPS-induced IL-6 and IL-8 production suggesting that IL-6 and IL-8 production is, in part, mediated by ERK 1/2 activation. Over expression of wild type β-arrestins 1 and 2 had no effect on LPS-induced ERK1/2 activation and LPS-induced IL-8 production suggesting that endogenous β-arrestins 1 and 2 are sufficient to mediate maximum ERK 1/2 activity and IL-8 production. β-Arrestins thus not only negatively regulate LPS-induced NFκB activation but also positively regulate ERK 1/2 activation and specific pro-inflammatory gene expression. Understanding the role of β-arrestins in regulation of TLR signaling pathways may provide novel insights into control mechanisms for inflammatory gene expression.